The invention relates to a solar collector device for the warming up of water, comprising a flat cylinder-shaped absorber element through which the water flows and made of temperature resistent black polymeric film material, on the sunside a cover element of at least one transparant polymeric film and on the shadowside an insulation panel. Such a collector device is known from U.S. Pat. No. 4,036,209. This type of collector device however has a low efficiency and is normally also not suitable for water temperature up to 95.degree. C.
With other known collector devices, designed to obtain a high efficiency, very often the absorber is embodied with extra provisions like fins and the like, in order to obtain the wanted heat transfer from the black absorber surface to the water to be warmed up. Apart from the cover elements often still made of glass and normally used to reduce the top losses of the absorber element, also a separate absorption coating is applied on the black absorber surface in order to reduce the reradiation (emission) from this surface. The investment costs of the above mentioned complicated solar collector devices, which are normally installed with an inclination angle, are high and because of the pressure differences concerned the costs for the water circulation through the absorber are not neglectable.
The invention has in view to solve the above mentioned problems and to provide a solar collector device, easily extendable over a large surface area, in which low costs and high efficiencies are combined.
With the solar collector device of the type, referred to in the beginning of this paper, this is achieved such that in the black polymeric film of the absorber element spectral-selective absorption pigment is embedded, and that an inner polymeric film is applied which has a high impermeability for water and water vapour, which latter film is composed in a laminate process with the black outer film to one integrated film. This inplementation gives the advantage that no separate spectral-selective absorption coating has to be applied on the outer surface of the absorber.
The inner film, preventing water vapour to escape from the absorber, can be made of metallised film.
The laminated absorber element can have a large length c.q. surface area, for which only in the longitudinal direction seals are needed as far as the absorber is not fabricated as an extruded cylinder. Because of the large wetted surface area of the absorber element also extra provisions like fins and the like for the heat transfer to the water are not needed.
With this new solar collector device, in which use is made of the flexible film material, the height of the water layer is determined by a water outlet header having a weir device of such a height with respect to the absorber element, that, in combination with the correct dimensioning of the water inlet and outlet openings, a water layer height of a few centimeters c.q. a water velocity of a few centimeters per second is obtained, which, maintaining with preference a turbulent flow, even with lengths of many tens of meters only creates a neglectable pressure difference across the absorber element.
On the shadowside the absorber element lies on an insulation panel.
From the water outlet header with weir device, mentioned earlier, the water is collected in an insulated collecting tank c.q. pump tank located just under the water outlet header. In those cases where a day/night storage is needed, this collecting tank can be extended under the full length of the insulation panel to a day/night storage tank, which can be incorporated simply in the integrated structure of absorber element, cover element and insulation panel.
The transparent cover element on the sunside of the absorber element consists of polymeric films, which in a simple fabrication process can be sealed in the longitudinal direction to one or more closed layer-shaped air space also of great length c.q. surface area. The closed space or spaces between the two or more transparant cover films is c.q. are filled up with a gas to the wanted layer thickness of a few centimeters for (further) reduction of the top losses of the absorber element. As said gas air, CO.sub.2, or a combination of both can be used.
For circumstances like existing outside tropical area's where the solar radiation angle can be less than 60.degree. with respect to the horizon, a reflection panel made of metallized polymeric film material can be applied in order to reflect the incoming solar radiation more rectangularly to the absorber element.
The investment costs per m.sup.2 of this solar collector device are approximately fifty percent of the costs of the solar collector devices available at the moment for the warming up of water up to a temperature of 95.degree. C. with a (similar) high efficiency.